Catalina Gneiss

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Geocache Description:

As you drive up the Catalina Highway to get to this earthcache, you will no doubt notice the color-banded rock that is exposed all along the road. This rock is called gneiss, and it is the most common rock type in the southern Santa Catalina mountains.

Gneiss is a metamorphic rock, which means that intense heat and pressure caused minerals in parent rock to recrystallize to form the gneiss. The gneiss in this area was formed from two different parent rocks. One parent is the Oracle granite from the Precambrian age. The other parent is the Wilderness Suite granite from the Eocene age. The Wilderness Suite granite is unusual in that, in addition to the minerals that are normally found in granite (feldspar, mica, and quartz), it also contains crystals of red garnet.

Between 35 and 20 millions years ago, the earth's crust in this region was stretched and sheared in a northeast-southwest direction. This movement introduced intense heat and pressure to the parent granites, which were buried at that time at a depth of seven to ten miles.

The heat and pressure deformed the granites. At temperatures of 600°F, the quartz crystals in the granite behaved like hot, soft plastic, and smeared into long ribbons in the direction of the crustal stretching. The feldspar crystals, which are more brittle at that temperature, were crushed and smeared, also in the direction of the stretching.

The long, aligned streaks of deformed minerals give the gneiss its unique texture. The light colored bands are considered to be deformed Wilderness Suite granite, while the dark colored bands are considered to be deformed Oracle granite.

How To Complete This Earthcache:

Bring a tape measure!

The posted coordinates lead you to a spot in the Santa Catalina mountains, where you will see some good exposure of the Catalina gneiss.

To get there, you need to take the Catalina Highway, which is a paved mountain road that runs north out of Tucson. There is a small fee ($5 or so) for recreational use. You completing an earthcache is recreational use.

At mile 4.5, you will reach the pullout for the Molino Canyon Vista. Plenty of parking is available. You will probably notice the exposed gneiss as you pull up to park. The elevation here is somewhere between 4000 and 5000 feet.

Park the vehicle and walk over to the coordinates. There you will see some very good examples of the gneiss.

Have Fun! Post A Photo Of Yourself. Sometimes, things become misguided. Earthcaches and geocaches are supposed to be all about the fun and the experience of the location, and about performing simple tasks and getting into the spirit of the earthcache. Try to embrace the original spirit of this earthcache and use one of the most powerful tools available to the field scientist - the camera. Try to take a photo of yourself with the exposed gneiss appearing in the background, and post it with your find log. A photo used to be listed as a requirement for this earthcache (prior to 15 May 2011), and as the past logs show, it was fully supported without any protest or controversy. It is a simple task that has always been completely reasonable, with everyone being supportive of it. However today, a photo is not required, due to the poor administrative practice of levying control over a small benign detail that affects nothing outside of the individual earthcache.

For this earthcache, a photo is simply requested, and is in line with the spirit of this earthcache. Click here to see a photo example. I don't care about your GPSr being in the picture.

LOGGING REQUIREMENTS:

In order to claim this earthcache as a find, you must complete the following tasks.

Requirement #1 - Measure And Estimate The Ratio Of The Rock: At the exposure at the coordinates, using your tape measure, measure the width of the light colored bands in the gneiss. Measure the width at several spots and determine the average. Then formulate answers to the following questions:
a) What is the average width of the light colored bands at this exposure?
b) You have seen a lot of exposed gneiss in roadcuts, etc. during your drive to this spot. Do you think that width of the bands in all the rock in this area is fairly constant and similar? Or is it widely varied (very wide at some spots and very narrow at others)?
c) From all the gneiss you have seen here, would you say that there is more dark colored mineral or light colored mineral in the gneiss? What would you say is the ratio of light to dark at the exposure at the coordinates? Do you think this ratio is fairly constant and similar for all the gneiss in the area, or does it widely vary?

Requirement #2 - Inspect And Compare: At the exposure at the coordinates, walk up and feel the gneiss with your fingers. Touch both the light colored and dark colored minerals. Get close and inspect both the light colored and dark colored minerals with your eyes. Answer the following questions:
a) What does the gneiss feel like? Be descriptive.
b) Can you feel a difference between the light colored mineral and the dark colored mineral? If so, what difference?
c) With your eyes, what do you see up close in the rock? Different particles? Different structure? Other than color, do you see a difference between the two minerals, or do they appear exactly the same other than color?